This invention relates to extreme UV radiation reflecting elements of extreme UV radiation generating devices. These devices are believed to play a great role for the upcoming “next generation” lithography tools of the semiconductor industry.
It is known that for extreme ultraviolet (‘EUV’) light, e.g., at wavelengths of around 20 nm or less, sometimes also referred to as soft X-rays, e.g., at 13.5 nm, reflective optical elements will be needed, e.g., for collecting and focusing the EUV light generated from a plasma created from a source material. At the wavelengths involved, either grazing angle of incidence or so called normal angle of incidence reflectors will be necessary for the collection and focusing of the light emitted from the plasma. The EUV radiation can be generated by an electric discharge produced plasma (‘DPP’) produced by an electrical discharge between a pair of electrodes or a laser produced plasma (‘LPP’) produced by a focused laser beam irradiating a target material to produce the plasma.
In the process of plasma generation to achieve the emission of EUV light several severe conditions of the plasma lead to mobilization of undesirable material into the environment in the EUV light source chamber that are potentially very damaging to optical components comprising, e.g., the collector element, e.g., heat, high energy ions and scattered debris from the plasma formation, e.g., atoms or particles of source related material. The heat, high energy ions and/or source material may be damaging to the optical elements in a number of ways, including simply heating them, penetrating into them (implantation) and, e.g., damaging structural integrity and/or physical optical properties, e.g., the mechanical and optical properties of the reflector operation to reflect light at such short wavelengths, corroding or eroding them and/or diffusing into them or allow for disadvantageous intermixing of components of the reflector.
In addition, the debris management for the EUV light source chamber may result in increasing the harshness of the environment in which the reflector needs to operate.